Process for converting hydrocarbon oils



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Aug. 18, 1936. E. PETTY ET AL PROCESS FOR CONVERTING HYDROCARBON OILS Filed March 22, 1935 Patented Aug. 18, 1936 P'nocnss Fon coNvsa'rnvG Himno- CARBON OILS Earl Petty, Scarsdale, and Hermann C. Schutt, North Tarrytown, N. Y., assignors, by menne assignments, to Gyro Process Company, Detroit, Mich., a corporation oi' Michigan Application March 22, 1935, Serial No. 12,370

7 Claims.

'I'his invention relates to the art of cracking hydrocarbon oils and more particularly to the recovery of a clean cracking stock from asphaltic or bitumen containing crude residuums and heavy tarry residuum of a cracking operation.

In the art of cracking, the amount of carbon in the stock being subjected to the cracking reaction determines the temperature limits and the economics of the process. Various methods have been used for segregating asphaltic and bituminous materials from the charging stock before it is subjected to the actual cracking reaction. For example, a clean primary distillate of low boiling range is sometimes used, or a residuum stock may be subjected to vacuum distillation to remove tar and carbonaceous materials. Still other systems combine the removal of carbonaceous materials with `the cracking operation by zoning the process of heating preparatory to cracking into operations which may be generally classified as strip-i ping, vacuum flashing, and viscosity breaking.y

None ofthese methods for the pre-treatment of an asphaltic or bitumen containing charge is capable of effecting a sharp separation of the bi- 4 tuminous material and the oil. The bituminous material is always removed in either a residuum tar, or fuel oil, or as coke. This method is inconvenient, inelcient, and results in a loss of potential yield in all commercial operations.

The method of this invention .provides a simple and effective means of overcoming these dinlculties by an economical and eilicient separation of the bituminous material without loss oi' valuable cracking stock. Heretofore the nearest approach to the method oi this disclosure has been accomplished by a complete coking operation at high temperatures. The method to be described hereinafter gives all the yield benets of the coking method andhas the advantage that the excess carbon, bitumen, asphalt, or, more generally, the low hydrogen to carbon ratio constituents are removed at low temperatures by means of a well known anti-solvent for such materials.

It is known that if the excess carbon is removed from a cracking stock that the optimumbalance of hydrogen to carbon may be obtained for conversion by the cracking reaction. By removing free carbon and the undesirable low hydrogen to carbon ratio constituents at a low temperature, the resultant product or rafllnate will be composed of constituents having a sufficiently high hydrogen to carbon ratio to give not, only improved yields of cracked products, but give improved ease of operation.

'Ihe lower the carbon number oi' a hydrocarbon solvent, such as naphtha, pentane, butane, propane, ethane or methane, the more effective does that material become as an anti-solvent for carbonaceous or bituminous materials.l When used in ratios, (liquidiof 4 to 8 times in volume, these anti-solvents are very eiective in precipitating at normal temperatures such carbonaceous mate- -rials as tar, asphalt resins, etc. Conversely, these liquids are selective and protective in affinity' for hydrogen. By selection of a solvent of the 10 proper carbon number, it is possible to separate from the charging stock only those constituents whose presence is most undesirable. For example, certain intermediate resins and naphthenic materials are valuable for cracking and it is desirable not to carry the separation too far, since the raiilnate may become even deilcient in carbon when the overall make-up oi' the material to be cracked is considered. Accordingly, it is preferred that a carbon anti-solvent of about the carbon number of butane or a solvent in which ybutane is predominant be used. Such a solvent will produce a ramnate having a proper .concentration of carbon and compounds of intermediate i hydrOgen to carbon ratio such as resinous asphaltines having some cracking value. If propane alone were used, these intermediate mate-' rials would be removed with the asphaltI carbon compounds.

It is an object of this invention to provide in a process for cracking hydrocarbon oils a method of establishing in the crackingstock an optimum ratio of carbon and hydrogen for the cracking reaction while eliminating and segregating the excess free carbon and low hydrogen to carbon ratio constituents from the cracking stock in zones c Vother than the high temperature heating and reaction zones. It is another object oi' this invention to provide in a vapor phase process for cracking hydrocarbon oils a method of increasing the degree of vaporization 'in the evaporator for the same temperatureand pressure conditions, to permit the use oi' higher operating temperatures in the viscosity breaking coil, to reduce the. amount of primary fuel oil residue produced, to secure a greater yield of gas oil equivalent charge to the vapor phase cracking coil, and to reduce the amount of light gas formed.

It is a further object of this invention to provide in a process for cracking hydrocarbon oils a method for controlling the asphaltic and/or bituminous constituency of the charging stock to permit a greater cracking per pass and produce the optimum quantity of refractory i'uel oil residue which when blended with the natural asphalt of the oil will give an improved specification fuel oil as regards cold test.

It is a still further object of thisinvention to provide in a process for cracking hydrocarbon oils a method for producing a more nearly oil free and wax free bitumen that can be produced by conventional distillate separation processes and recovering the oil wax bearing fractions as cracking stock.

It is a further object of this invention to provide in a process for cracking hydrocarbon oils a method for producing from the bituminous constituents of the oil, a specification fuel oil of low cold test.

In the accompanying drawing which forms part of the instant specification and is to be read in conjunction therewith, the single figure is a schematic view of one form of apparatus capable of carrying out the process of this invention.

In general, the processof this invention contemplates the treatment of a cracking stock such as, for example, an asphaltic or bitumen containing reduced crude witha liqueed, normally gaseous hydrocarbon solvent and the separation from the cracking stock of insoluble free carbon, natural asphalt and bitumen to secure a gas oil equivalent charge for passage to the high temperature heating and reaction zones. These constituents forming the separated extract will be hereinafter referred to .more generally as low hydrogen to carbon ratio constituents, it being understood, however, that this term is intended to include free carbon as well as asphaltic compounds having a low hydrogen to carbon ratio.

The clean charging stock or ramnate is then passed to a relatively low temperature heating or mild cracking zone where, if necessary, the ramnate may be subjected to a viscosity breaking operation and then ashed into a light vapor fraction and a relatively heavy liquid fraction forming a primary fuel oil. The light fraction is subjected to a relatively high temperature or more drastic cracking reaction after whichthere is separated from the cracked products a refractory fuel oil of low viscosity and high solvent power. The remaining vapor fraction of the cracked products is fractionated to recover a light distillate such as, for example, a motor fuel of gasoline boiling range.

The primary iuel isfiashed atreduced pressure to recover the light gas oil remaining therein which is condensed and returned to the fractionator. The remainder of the primary fuel and the refractory fuel is passed to the solvent extraction zone wherein further separation of the fuels is made to recover a gas oil equivalent cycle stock while the asphaltic or bituminous constituents are rejected and removed with similar constituents of the fresh charge as a substantially oil and wax free bitumen.

If a residual operation is desired for the production of a low cold test fuel oil, the residue of the primary fuel is subjected to solvent extraction as has been described above while the refractory fuel is used for blending with the bitumen separated from the fresh charge and/or the primary fuel to form by virtue of its high solvent capacity a fuel oil of extremely low cold test.

Referring now more particularly to the drawing, the charging stock consisting of, for example, an asphaltic reduced crude, is fed through a line I to a pump 2 which discharges the oil under pressure through a line 3 controlled by a valve 4 to a heat exchanger 5. The charging stock is heated in this exchanger and is discharged therefrom through a line 8 controlled by a valve 1 to a flash or distillation tower 8 wherein a separation of the oil into vapors and unvaporized oil takes place. lThe flash tower may be provided with a suitable number of baille plates or fractionating trays and the degree of vapcrization may be controlled by means of a heating coil in the tower to which steam or other heating medium may be admitted through a line 9 and be removed through a line I0.

The unvaporized oil, free of those light ends suitable as cracking material without solvent treating, is withdrawn from the flash tower 8 through a line II and is pumped by pump I2 at a pressure of from 100 to 150 lbs. per square inch through a heat exchanger I3, wherein the oil is slightly cooled and then passes through a line I4 to a conventional reboiler I5 of a solvent stripping tower 54 where some of the heat of the untreated oil is given up in stripping solvent from treated oil. The further cooled oil leaves the reboiler through a line I6, passes through a heat exchanger I1 wherein it is further cooled by indirect heat exchange with oil-solvent solution passing to the stripping tower, and on leaving the heat exchanger I'I passes through a line I8 and cooler I9 to a mixing chamber 20. A flnal cooling of the oil to a favorable solvent treating ltemperature, for example 70120 F., is effected in the cooler I9. The mixing chamber 20 may be equipped with suitable bailles, or mechanical agitating devices (not shown) for securing proper admixture of oil and solvent, solvent under pressure being introduced to the mixing device through a line 2l. A liquefied, normally gaseous hydrocarbon such as butane, or butane admixed with varying proportions of lighter normally gaseous hydrocarbons, is used as the solvent. The specific references to a particular hydrocarbon solvent arer illustrative only, and it will be understood that the character of the charging stock as regards its content of asphaltic or bituminous concentrates, the percent of resinous naphthenes Whose removal is desired, and/or the desired freedom of asphalt from oil will govern the character and amount of the solvent to be used. However, sunlcient of a selective solvent should be admixed with the oil to precipitate the amount and kind of constituents not suitable for cracking it is desired to remove and the ratio orf solvent to oil may be, for example, four to ten parts of solvent by volume to one part of oil.

The oil-solvent mixture containing insoluble constituents leaves the mixing device 20 and passes under pressure through aline 22 to a bitumen separator or settling tank 23.

The separator 23 is of suillcient size to permit the establishment of the time element necessary to secure separation of the insoluble constituents from the oil solvent solution. The bitumen collects in the lower portion of the separator while the supernatant oil solvent solution free of bitumen forms a layer above the bitumen. A baille 24 or other suitable device for preventing intermixture of the bitumen and oil is suitably positioned within the separator.

'I'he bitumen collecting in the bottom of the separator 24 discharges through a line 25 to the suction side of a pump 26. The pump may be manually controlled or automatic means diagrammatically indicated at 21 may be'provided for controlling the pump and the withdrawal rate in accordance with the viscosity of the bitumen being removed. The bitumen is forced by means oi' the pump 26 through a line 28, through the heat exchanger I3, picking up a -certain amount of heat from the hot untreated oil dischargedfrom the fiash tower 8 and then is forced through a line 29 to a ysolvent stripping tower 38 wherein by the application of heat, solvent is distilled from the bitumen, the solvent vaporsunder considerable pressure passing overhead through a line 3|, being condensed in a condenser 32 and the liquid discharging into a pressure accumulator 33. The stripping tower 38 is provided with `a heating coil, steam or other suitable heating medium being introduced thereto through a line 34 and removed through a line 85.

The pressure accumulator 33 is maintained at the desired condensing pressure by means of a back pressure control valve 36 in a vent line 31. 'Ihe solvent liquid accumulating in the accumulator 33 discharges therefrom under pressure through a line 38 being returned thereby tothe line 2| for reusein the system.

The bitumen in the tower 38 free of wax oil and solvent discharges from the tower through a line 39 controlled by a valve 48 and passes therefrom through a line 4| to storage tanks (not shown).

'I'he bitumen free oil solvent solution in the separator 23 overflows into an internal chamber 42 in which a constant liquid level, is maintained by a liquid level control device generally indicated at 43. The oil solvent solution discharges from Vthe chamber 42 through a line 44 to the suction side of a pump 45. Although the pump 45 may be manually controlled, it is preferably controlled by the liquid level control device 43 in a manner well known in the art. The oil solvent solution is discharged under considerable pressure by the pump 45 through a line 46 and passes through the heat exchanger |1 from which it passes through a line 53 to a solvent stripping tower 54.

Although we have shown a bitumen separator 23 functioning to remove the bitumen from the oil solvent solution by gravity, it is within the contemplation of our invention to substitute therefor a continuous centrifugal separator operating under pressure.

Solvent is stripped from the solution in the tower 54 by means of the reboiler i 5 and a heating coil into which a heating medium is fed from a line 64' and `removed through a line 65. I'he solvent vapors pass overhead through a line 55, being condensed in a cooler 56, the condensate passing to a pressure accumulator 51 in which a back pressure is maintained by means of a pressure regulator 58 in-a gas Jlentrline 58. The solvent liquid discharges under pressure from the accumulator 51 and passes through a line 68 to the line 2| for reuse in the process. Further solvent may be added to the line 2| through a line 6| connected to a`source of solvent supply by manipulation of the control valve 62.

The treated oil is discharged under the pressure in the solvent stripping tower 54 through a line 63 controlled by a valve 64 and fed to a fractionating tower 65 equipped with the usual fractionating trays 66. At the same time oil vapors separated from the charging stock in the flash tower 8 are fed through the line 81 to the fractionator 65.

The hot liquid bottoms in the fractionatlng tower are withdrawn through a line 68 by means of a pump 69 and pumped through a line 18 through the heat exchanger 5 to impart heat of the valves 1.and 14 in the lines 6and'3 .respectively, permitting part of the kcharging stockto flow from the line 3 through a line 12 controlled by a valve 13 to the fractionating tower 65.

The bottoms in thefractionating tower-aconsisting of reflux condensate,l cycle stock,V andvl` charge oil are lwithdrawn througha line,16 and pumped by means of the pump 11 through aline 18 to a low temperature primary heating, viscosity breaking, or mild cracking section 19 of a cracking furnace 88 from which the heated oil discharges through the line 8| toa primary-evaporator 83 at a lower pressure, provided-with a suitable vnumber of fractionating trays 84. The pressure on the oil discharging through the line 8|A is reduced by means of a reducing valve 82 so that a controlled amount of .flash vaporization will take place in the evaporator 83 due to th sensible heat of the hot oil.

The vapors evolved in the evaporator 83 pass off overhead through a line 85, through a high temperature vapor phase cracking section 86 of the cracking furnace 88, discharging therefrom through a line 81 to an arrester 88. The vapors are quenched in the arrester 88 below active vapor phase cracking temperature by means of a cool hydrocarbon oil, the quenched products passing through a. line 89 to a flash tower 98 equipped with a suitable number of fractionating trays 9|.

A clean side stream distillate is withdrawn from a suitable tray of the fractionating tower 65 through a line 92,.a portion being pumped by means of a pump 93 through a cooler 94, the cooled distillate being diverted in part through a line 95 controlled by a valve 96 to the arrester 88 for use as the quenching medium. The remainder of the cooled distillate passing through the line 92 is fed through a line 99 controlled by a valve |88 to the flash tower 98 where it serves as reflux for endpoint control and to knock back heavy ends unsuitable for recycling. Another portion of the side stream is diverted through aline 91 controlled by a valve 98 to the primary evaporator 83 wherein the cooled side stream acts as reflux for fractionation control in the same manner.

The light vapors passing overhead from the flash tower 98 are removed through a line |8I, and introduced at a suitable point into the fractionating tower 65 wherein a separation of cycle stock from the vapors is carried out.

The unvaporized oil in the ash tower 98 generally unsuitable for recycling because of its low hydrogen to carbon ratio consists of a refractory fuel oil which because of its comparatively low viscosity has a high blending power and is withdrawn therefrom through a line |82 and may, if desired, be diverted without further treatment through the line |83 controlled by a valve |84 to storage tanks (not shown). However, if solvent treatment of this refractory fuel oil is desired for the purpose of recovering additional cracking'stock therefrom, it may be diverted from the line |82 through a line |85 and pumped by means of a pump |86 through aline |38 controlled by a valve |3| and returned through a line |21 controlled by a valve |29 to the flash tower 8. This fuel oil'bein'g at a relatively high temperature will aid in vaporizing the light ends v control on the fractionating trays ||2.

of the untreated refractory fuel oil may be advantageously utilized by diverting the oil from the line |05 through a line |01 joining the line 4| by opening a valve |08 in the line |01 and closing the valve |3| in the line |30, the oil thus being blended with oil and wax free'bitumens recovered by solvent treating of the charge and/or primary fuel oil and issuing fromthe solvent stripping tower 30 through the line'38 to form a 4 blended specification fuel oil of low cold test.

The primary fuel oil in theevaporator 83 discharges under pressure through a line |09 con- 1trolled by a valve ||0 to a secondary evaporator provided with a suitable number of fractionating trays .l 2. This secondary evaporator is preferably maintained at a somewhat lower pressure than exists in the primary evaporator 83 and there will be, therefore, a flash vaporization occurring, oil vapors passing overhead through a line ||3 controlled by a valve ||4, through a condenser ||5, condensate formed therein being collected in a reflux accumulator H8. Condensate is withdrawn from this accumulator through a line H1 and is pumped in part by means of a pump IIB, through a line ||9 controlled by a valve |20 to the secondary evaporator to serve as reflux for endpoint The remainder of the condensate is pumped through a line |2| controlled by a valve |22 to the fractionating tower 85 for recycling in the cracking furnace.

The unvaporized fuel oil in the secondary evaporator still contains some heavy cycle stock and being at a comparatively high temperature, is withdrawn through a line |24 and, if desired, may be passed without further treatment through a line |25 controlled by a valve |26 to storage tanks (not shown).

Preferably, however, since this fuel oil still contains considerable cracking stock whose recovery is desirable in order to maintain a high yield the fuel oil is lpumped through a line |21 by means of a pump`|28 to the flash tower 8 for recycling Vto the solvent treating plant, its heat content being imparted to the fresh feed and aiding in the distillation of the initial charging stock if'this material is also being subjected to soiventtreatment. If desired, this fuel oil in pipe |21vmay be fed through a pipe |50 into pipe |4 by opening rvalve |5| and closing valve |52 in pipey|21 thusbypassing the flash tower 8 in densed in a cooleri33, the condensate and vapors being collected in a reflux accumulator |34. Reflux is returned from this accumulator through aline |35 by means of the pump |36 to the fractionating tower 65. The vapors passing overhead from the accumulator |34 are removed through aline |31, are condensed in a final cooler |38, and accumulated in a separator |39. The uncondensable gases are removed through a line |40, a back pressure being maintained by a regulating valve- |4 the distillate being removed as a liquid from the separator |30 through the line |42 and passed to a stabilizer feed tank (not shown).

It will be observed that we have accomplished the objects of our invention and have provided al distillation methods and by which a fuel oil of low cold test is secured by blending the low viscosity refractory fuel oil with the wax-free bitumen separated by solvent extraction. We are also enabled by our process because of the lesser amount of low hydrogen to carbon ratio hydrocarbons to secure an increased yield of lower boiling hydrocarbon distillate of high octane from the original charging stock by using higher temperatures without danger of coke deposition in the conversion coils.

It will be understood that certain featuresand sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of' our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specic details shown and described.

Having thus described the invention, what we claim is:

1. A process for cracking hydrocarbon oil comprising treating charge oil with a diluent in which bituminous constituents. of the oil are substantially insoluble, removing the undissolved constituents from the oil, fractionating the treated oil in a fractionating zone, subjecting reflux condensate withdrawn from the fractionating zone to mild pyrolytic conversion in a relatively low temperature conversion zone, separating the heated oil into a primary residue and a relatively light fraction, subjecting the light fraction to more drastic pyrolytic conversion in a relatively high temperature conversion zone, separating the products of the high temperature conversion operation into a light fraction and a relatively heavier secondary residue, returning the last mentioned light fraction to the fractionatlng zone, withdrawing the secondary residue from the process and combining the primary residue with the oil passing to the solvent treating zone.

2. The process of claim 1 wherein the diluent comprises normally gaseous hydrocarbons.

3. The process of claim 1 including the step of blending the secondary residue with the insoluble constituents removed from the oil to form a low cold test fuel oil. .Y

4. A process for cracking hydrocarbon oil comprising distilling fresh oil in a distillation zone and there separating the oil into vapors and unvaporized oil, separately removing the vapors and unvaporized oil from the distillation zone, treating the unvaporized oil with a solvent in which the oil constituents relatively rich in hydrogen are soluble and constituents relatively poor in hydrogen are substantially insoluble, separating the undissolved compounds from the oil-solvent solution, distilling the solvent from the oil, fractionating the solvent free oil in a fractlonating zone, passing a stream of reflux condensate from the fractionating zone to a heating zone and subthe high temperature cracking reaction into a vapor fraction and a secondary residue, fractionating the vapor fraction in the fractionating zone, and distilling the primary residue in the distillation zone.

5. The process of claim 4 including the step of combining the primary residue with the u'nva.- porized oil removed from the distillation zone rather than with the fresh oil in the distillation zone.

6. The process of claim 4 including the step of heating the fresh oil by heat exchange relationship with reux condensate from the fractionating zone before introducing the fresh oil to the distillation zone.

7. The process of claim 4 including the step of distilling the solvent from the undissolved constituents separated from the oil solvent solution and blending these constituents with the secondary residue to form a low cold test fuel oil.

.EARL PETI'Y.

HERMANN C. SCHU'I'I'. 

